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Two series of experiments were conducted to examine the utilization of exogenous sperm and their degree of depletion in three hermaphroditic sea hares, Aplysia kurodai Baba, 1937, A. Juliana Quoy & Gaunard, 1832, and A. parvula Guilding in MOrch, 1863. The first series of experiments was designed to determine whether one mating is enough for female partners to receive sufficient sperm to fertilize at least one egg mass. For this purpose, isolated individuals were mated as females once with conspecific individuals and the viability of their subsequent eggs was examined. When successfully...

Two series of experiments were conducted to examine the utilization of exogenous sperm and their degree of depletion in three hermaphroditic sea hares, Aplysia kurodai Baba, 1937, A. Juliana Quoy & Gaunard, 1832, and A. parvula Guilding in MOrch, 1863. The first series of experiments was designed to determine whether one mating is enough for female partners to receive sufficient sperm to fertilize at least one egg mass. For this purpose, isolated individuals were mated as females once with conspecific individuals and the viability of their subsequent eggs was examined. When successfully inseminated, individuals of all the three species received enough sperm to fertilize at least one egg mass, and they continued to lay 3.6–8.5 viable egg masses. However, 10–36% of the matings by these sea hares did not result in any viable egg production by the female partner, indicating that these matings did not involve sperm transfer Such matings without sperm transfer tended to be shorter than matings with successful sperm transfer The second experimental series was conducted to examine whether sperm depletion actually occurs or not in field-caught adults. For this purpose, adult individuals caught in the field were allowed to lay eggs under isolated conditions without mating All the individuals of A. kurodai and A. juliana stored enough sperm to fertilize at least one egg mass. However, in A. parvula, 23–33% of individuals laid egg masses containing non-viable eggs at their first spawning after isolation, indicating that these individuals were depleted in exogenous sperm